Transparent substrate such as glass is used for vehicular window glass, architectural window glass, lens, goggles, etc. In case that glass is used in a high-humidity place or at a boundary of a large temperature difference and a large humidity difference, however, there occur condensation and fogging on the surface. For example, in case that a vehicle is run in a high-humidity rainy season or in a low-temperature winter, the generation of the window fogging is inevitable. It is generally conducted to allow a dehumidifying wind, such as warm wind or cold wind, to blow against the window to make it in a dry condition in order to secure the visibility.
Therefore, a large energy is consumed for securing the visibility of window, and it has been a limitation in improving vehicular fuel consumption characteristics. In particular, a larger energy is consumed for securing the visibility of window in a winter season, in which the temperature difference between interior and exterior becomes great, particularly in a cold place that can have a below-freezing-point environment. Furthermore, there are also problems such as the increase of uncomfortableness of vehicle interior by making it in a dry condition. It is essential for environment and human-friendly vehicles to provide a window glass that can reduce these problems, that is, an antifogging article. Furthermore, the necessity of antifogging articles is expected to become higher in electric vehicles such as hybrid automobiles and fuel-cell automobiles.
As a vehicular antifogging glass, Patent Publication 1 discloses an antifogging vehicular glass prepared by applying a composition containing an organic antifogging material to a low ultraviolet transmission glass. Patent Publication 2 discloses a vehicular window glass having an interior surface, on which a hydrophilic layer that contains alumina and has a contact angle with of 30° or less to a water drop is formed.
Means for showing antifogging property in these publications are, however, mainly by a water film formation of a hydrophilic layer. Therefore, there occur defects such as one in which the image through the water film upon showing antifogging property is distortedly seen. Furthermore, the water film is frozen in a below-freezing-point environment. For melting the frozen water film, there rather occur problems such as one in which the energy consumption for the warm wind blow is necessary.
Patent Publication 1 discloses the use of a silica fine-particle series porous film and a water-absorbing resin as ones for showing antifogging property by water absorption property. The water absorption capabilities of these water absorptive films have not been enough, and further improvements have been necessary to show antifogging property by water absorption property. In addition, since there is no design from the viewpoint of showing antifogging property in a below-freezing-point environment, it is also expected to have a possibility of having defects such as the light transmission reduction and the film destruction by freezing of the absorbed water.
Under such background, the present applicant has proposed an antifogging glass suitable for a vehicular window that makes the window visibility securement easy even in a cold place that can be a below-freezing-point environment (Patent Publication 3). The antifogging glass uses a film by a urethane resin having hydrophilicity and water absorption property. The antifogging property is designed to show antifogging property first by water absorption of the film and to continue antifogging property by hydrophilicity of the film after water absorption saturation. Furthermore, it has a superior scratch resistance by elasticity inherent in urethane resin.    Patent Publication 1: Japanese Patent Application Publication 2000-239045    Patent Publication 2: Japanese Patent Application Publication 2003-321251    Patent Publication 3: Japanese Patent Application Publication 2005-187276